When a side impact occurs, from one side of the vehicle, the vehicle is given a very sudden acceleration. The effect is that, due to inertia, occupants of the vehicle tend to move towards the side of the vehicle where the impact occurs.
Typically a vehicle occupant is restrained by a three-point seat-belt. Typically a three-point seat-belt has a lap belt portion and a diagonal shoulder belt strap, the shoulder belt portion typically extending from a point adjacent the centre of the vehicle upwardly across the chest or torso of the occupant to a point on the adjacent “B”-Post of the vehicle for a front seat passenger and “C”-Post of the vehicle for a rear seat passenger.
In the case of a side impact for a vehicle occupant who is sitting adjacent the side of the vehicle where the impact occurs, the effect will be that the torso of the occupant will tend to move towards the side of the vehicle where the impact occurs. The shoulder of the occupant will thus be “caught” by the shoulder belt portion and the occupant will be restrained. However, for a seat occupant sitting on the side of the vehicle furthest from the side impact, the torso of the occupant will tend to move away from the adjacent “B”-Post, and will not be restrained to a substantial extent by the shoulder belt strap.